Work feed control

ABSTRACT

In a sewing machine having a work feed plate for supporting and reciprocally moving an article to be sewn between first and second positions beneath the sewing head of the machine at varying speeds and in a predetermined sequence in order to vary the spacing between stitches sewn into the article, means is provided for reciprocating the plate in accordance with the predetermined sequence, which means includes a double acting hydraulic ram or air cylinder applying a uniform pressure to the plate to move it between its first and second positions and means for variably resisting movement of the plate in accordance with the predetermined sequence to vary the speed of movement of the plate from its first to its second position. The resisting means includes a hydraulic control cylinder having at least two ports therein, a fluid reservoir in communication with the cylinder through the ports and a plunger in the cylinder operatively connected to the plate and cooperating with fluid in the cylinder to resist movement of the plate. The plunger initially returns fluid in the cylinder to the reservoir through only one of the ports, then through both ports and finally through only one port so that movement of the plate is variably resisted and the plate is moved faster between the first and second position when fluid is returned to the reservoir through both of the ports than when fluid is returned to the reservoir through only one of the ports.

United States Patent 1 1 McKeen 1 51 June 5,1973

[54] WORK FEED CONTROL [75] Inventor: Leighton R. McKeen, El Paso, Tex.

[73] Assignee: Farah Manufacturing Company, Inc., El Paso, Tex.

[22] Filed: Nov. 3, 1971 [21] Appl. No.: 195,240

52 u.s.c1 ..112/203,188/318 51 int. c1. ..D05b 27/00 [58] FieldofSearch ..112/47,90,102,

[56] References Cited UNITED STATES PATENTS Primary ExaminerWerner H. Schroeder Att0rneyCurtis, Morris & Safford [57] ABSTRACT In a sewing machine having a work feed plate for supporting and reciprocally moving an article to be sewn between first and second positions beneath the sewing head of the machine at varying speeds and in a predetermined sequence in order to vary the spacing between stitches sewn into the article, means is provided for reciprocating the plate in accordance with the predetermined sequence, which means includes a double acting hydraulic ram or air cylinder applying a uniform pressure to the plate to move it between its first and second positions and means for variably resisting movement of the plate in accordance with the predetermined sequence to vary the speed of movement of the plate from its first to its second position. The resisting means includes a hydraulic control cylinder having at least two ports therein, a fluid reservoir in communication with the cylinder through the ports and a plunger in the cylinder operatively connected to the plate and cooperating with fluid in the cylinder to resist movement of the plate. The plunger initially returns fluid in the cylinder to the reservoir through only one of the ports, then through both ports and finally through only one port so that movement of the plate is variably resisted and the plate is moved faster between the first and second position when fluid is returned to the reservoir through both of the ports than when fluid is returned to the reservoir through only one of the ports.

14 Claims, 5 Drawing Figures WORK FEED CONTROL This invention relates to a device for regulating the speed of movement of a reciprocating work element, and more particularly, to a speed regulator for a reciprocating work feed plate of a sewing machine, which regulator varies the speed of movement of the plate in accordance with a predetermined sequence.

When sewing clothing or other articles, it is often desirable to vary the stitch spacing or pattern along a line of stitches in order to provide more strength at certain areas of the sewn work piece. For example, at either end of the back pocket opening or lip of a pair of pants it is necessary to have greater strength, and therefore more stitches. The increased stitch density at the ends of the pocket lip assists in preventing stitches from breaking during normal usage and extends the life of the article.

Previously, the density of stitching was controlled by the operator as he manually fed the fabric past the reciprocating needle in the sewing machine. By controlling the speed at which he manually fed the fabric past the needle the operator was able to control the density of the stitches sewn into the article. Other devices for controlling the stitch density require an intermittently operating rotating fluid valve of considerable complexity as shown in U. S. Pat. No. 3,572,266.

In accordance with an aspect of the present invention a sewing machine is provided with a reciprocating work feed plate on which the fabric or article to be sewn is supported and moved past the reciprocating needle of the machine. A speed regulator is provided for the reciprocating plate in order to move the plate between first and second positions at varying speeds and in a predetermined sequence thereby to vary the spacing between the stitches sewn into the fabric. The regulating means includes a hydraulic ram or air cylinder operatively connected to the plate, which ram applies a uniform force to move the plate between its first and second positions. Means is provided for resisting movement of the plate by the ram with a varying force applied in accordance with the predetermined sequence in order to vary the speed of movement of the plate from its first to its second position.

The resisting means includes a, hydraulic control cylinder having at least two ports therein. A plunger is provided in the cylinder which is operatively connected to the work feed plate for movement therewith under the force exerted by the ram between first and second positions corresponding respectively to the first and second positions of the plate. The plunger is formed with first and second spaced and operatively interconnected pistons that define therebetween a first fluid chamber in the cylinder. The pistons are adapted to open selectively and close one of the ports therein.

A reservoir containing hydraulic fluid is connected to the cylinder ports by independent conduits having fluid flow restrictors therein. The first port of the cylinder is located for selective communication with the chamber defined between the spaced pistons and the second port is located for communication with a second fluid chamber defined between the first piston and the adjacent end of the cylinder. The first piston has bleed bores formed therein to provide communication between the first and second chambers in order to equalize fluid pressure therein. The pistons cooperate with the fluid in the cylinders to resist movement of the plate by the ram in accordance with the predetermined sequence as follows:

At the first position of the plate and plunger, the first piston closes the first port of the cylinder and as the plunger is moved from the first position to the second position, the first piston forces fluid in the second chamber through the second port. As the first piston moves away from the first port, that port opens to provide communication between the reservoir and the first chamber and the second piston then begins to force fluid in the first chamber through the first port to the reservoir while the first piston continues to force fluid to the reservoir through the second port. As a result, the resistance to movement of the plate is decreased and the speed of movement thereof is increased. As the plunger approaches its second position, the second piston closes the first port while the first piston continues to force fluid to the reservoir through the second port so that resistance to movement of the plate is increased and the speed of movement of the plate is decreased, whereby the spacing between the stitches is decreased to provide a more dense stitching pattern.

The above, and other features and advantages of this invention will be apparent in the following detailed description of illustrative embodiments thereof which are to be read in connection with the accompanying draw ings wherein:

FIG. 1 is a schematic illustration of the resultant switch pattern produced by the work feed plate and speed regulator of the present invention;

FIG. 2 is a schematic side view of one embodiment of the work feed plate and speed regulator of the present invention, in the first position of the plunger;

FIG. 3 is a schematic view similar to FIG. 2 of another embodiment of the present invention illustrating the position of the plunger after the initiation of movement of the work feed plate from its first to its second position;

FIG. 4 is a schematic illustration similar to FIG. 2 illustrating the configuration of the plunger just prior to the work feed plate and plunger achieving their respective second positions; and

FIG. 5 is an illustration of the configuration of the plunger with respect to the cylinder at the second position of the plunger and the work feed plate.

Referring now to the drawings in detail and initially to FIGS. 1 and 2 thereof, it will be seen that a work feed plate speed regulator 10 embodying the present invention as shown therein includes a hydraulic ram or pneumatic cylinder 12 and a speed or resistance control assembly 14 which are operatively connected, through a schematically depicted linkage 16, to a work feed plate 18.

Work feed plate 18 is positioned on a pair of spaced apart rails 20, only one of which is seen in the drawings, for sliding movement between a first and a second position. Linkage 16 includes an oscillating control rod 22 pivotally connected at 24 to the underside of plate 18, between rails 20. The opposite end 26 of link 22 is pivotally mounted at 28 on a support block 30, properly positioned with respect to the sewing machine (not shown).

Ram 12 and control assembly 14 are operatively connected to link 22 in any of a number of relative configurations, as more fully described hereinafter, and are operative to reciprocate plate 18 along rails 20 between its first and second positions in accordance with a preplied to the fabric. In the preferred embodiment of the present invention, the work feed plate 18 is moved relatively slowly at the initial and final portions of its movement and more rapidly during the intermediate portion of movement so that, as shown in FIG. 1, an initial dense section of stitches 32 is formed at the beginning of the fabric. The increased speed of plate 18 during the intermediate portion of its movement causes the stitches formed in intermediate section 34 to be more widely spaced. As plate 18 is slowed down towards the end of its movement, a final dense section of stitches 36 is formed. As mentioned above, this configuration of stitches is preferably for sewing back pockets into slacks and the like, since the edges of these pockets when secured to the pants are subjected to relatively high stresses and the additional strength provided by the denser stitches is required.

Ram 12 is a double acting hydraulic or pneumatic cylinder having a piston therein (not shown) to which is connected an actuating rod 38 that is reciprocated by movement of the piston within the ram. Ram 12 is adapted to apply a relatively constant force to move rod 38, in either direction, and the latter is operatively connected to link 22 to reciprocate plate 18 along rails 20. In an illustrative embodiment of the invention, seen in FIG. 2, rod 38 includes a plunger section 40 enclosed within a control cylinder 42. Plunger 40 includes an extension 44 which passes through an opening 46 in cylinder 42 and is pivotally connected to link 22. Plunger 40 forms part of control assembly 14 and provides variable resistance to the movement of actuator 38, and thus the piston within ram 12, in order to vary the speed at which link 22 is oscillated and thereby the speed at which plate 18 is reciprocated. It is to be understood that the pivotal connections 24 and 48 illustrated in the drawings are schematic, and that these connections are constructed in a conventional manner to permit sliding motion between link 22, plate 18 and extension 44 in order to accommodate the slight arcuate motion of these pivot points. Such a connection is well known to mechanics in the art of reciprocating motion and need not be described here in detail.

It is also to be understood that ram 12 may be connected to link 22 in a variety of manners. One such connection is illustrated in FIG. 3 wherein actuator rod 38 is directly connected to link 22 by a pivotal connection 50. The control assembly 14 herein remains the same in structure and operation with the pivotal connection 50 being adopted to accommodate sliding movement between actuator 38 and link 22 as the pivot point 50 moves in a slightly arcuate path. Similarly, as will be clear to those skilled in the art, ram 12 and control assembly 14 may be connected independently to link 22 as long as control assembly 14 is positioned as described hereinafter to resist the movement of actuator 38 from the first position of plate 18 to the second position thereof.

Returning again to FIG. 2 of the drawings, control mechanism 14 includes first and second ports 52 and 54 through which fluid 56 contained in a reservoir 58 is supplied to cylinder 42. Reservoir 58 is connected to cylinder 42 by conduits 60 and 62 respectively. Each of these conduits includes a restrictor 64 of conventional construction which restricts the flow of fluid from cylinder 42 to the reservoir 58.

Plunger 40 includes a pair of piston sections 66 and 68 which define a first chamber 70 therebetween within'cylinder 42. Piston 68 defines a variable volume chamber 72 between face 74 thereof and the end wall 76 in which port 54 is formed. These pistons serve to sequentially return fluid in cylinder 42 to reservoir 58 through one or both of conduits 60 and 62, thereby controlling the speed of movement of plate 18.

In the first position of plate 18, actuator rod 38 is retracted by ram 12 and plunger 40 is located in the position illustrated by FIG. 2. Chambers 70 and 72 are, in this configuration, filled with fluid supplied from reservoir 58 and the pressure therein is equal because of the bleed bores 78 formed in piston 68, which bores provide intercommunication between the two chambers. In order to move plate 18 from its first to its second position, ram 12 is operated to extend actuator rod 38, that is, to move the rod towards the right in FIG. 2. In the first position, piston 68 closes port 52 and prevents fluid from flowing therethrough. As actuator 38 is extended, the face 74 of piston 68 increases the pressure on the fluid contained within chamber 72 and, since the fluid is incompressible, urges it through conduit 62 and restrictor 64 to reservoir 58. The pressure within chamber 70 and 72 remains the same because of bleed ports 78 and plunger 40 slowly moves to the right, whereby member 44 pivots link 22 about pivotal mounting 28. As plunger 38 is extended, piston 68 eventually moves to the configuration illustrated in FIG. 3, wherein port 52 is open to chamber 70. At this point, since the pressure within chambers 70 and 72 is the same, the fluid contained within these chambers is forced by the movement of pistons 66 and 68 through both ports 52 and 54, through conduits 60 and 62 and the restrictors 64 therein. As a result an adjustable rate of fluid flow, e.g. twice as much fluid flows from chamber 72, and thus less resistance, is afforded to the motion of actuator 38 and to the reciprocation of link 22. Plate 18 therefore moves faster through this portion of its path of travel than during the initial portion thereof when port 52 is closed. Thus, the spacing between stitches is wider during the portion of movement of plate 18 when both chambers 70 and 72 are open to reservoir 58.

During the travel of the plunger from the configuration in FIG. 3 to the configuration in FIG. 4, when forced by actuator 38, the velocity of plate 18 is constant and the wide spacing of the stitches is achieved. However, as plunger 40 continues to move toward the right past the point illustrated in FIG. 4, port 52 is closed by piston 66 and fluid is thereby prevented from flowing through this port to the reservoir. This configuration is illustrated in FIG. 5. As a result of closing port 52, continued movement of plunger 40 to the right will only force fluid through port 54 and restrictor 64 to reservoir 58, thereby increasing the resistance to movement of actuator 38 to the right, to the same level which existed during the initial portion of movement of the plunger. Accordingly, link 22 and thus plate 18 are moved more slowly towards the second position of the plate and the dense stitching section 36 is formed at the end of the stitching line.

While in the illustrative embodiment of the present invention, dense stitching is provided at both ends of the stitch pattern, by closing port 52 at the beginning and ending of movement of plunger 40, it is to be understood that movement of actuator 38 and thus plunger 40 may be stopped before port 52 is closed by piston 66. In this case, the dense stitching will occur only at one end of the stitch pattern. This arrangement is useful in a number of applications, as for example when sewing buttonholes.

When ram 12 is fully extended and actuator 38 is moved all the way to its extreme right position, as illustrated in FIG. 5, the sewing operation is completed and actuator 38 is retracted in preparation for the next sewing operation.

In order to facilitate retraction of ram 12, and to assure that chamber 72 is rapidly refilled from reservoir 58, so that the speed of operation of the sewing machine is not seriously affected, conduit 62 is provided with a bypass 80 having a check valve 82 therein. Check valve 82 prevents fluid flow through bypass 80 during movement of plunger 40 to the right. However, as the plunger is returned from the configuration illustrated in FIG. 5, to the configuration illustrated in FIG. 2, the pressure in chamber 72 decreases and check valve 82 opens so that fluid flows from reservoir 58 through the valve and into chamber 72 without restriction. By the time plunger 40 is fully retracted chamber 72 is filled with fluid and the device is ready for operation again.

Thus, it is seen that a relatively simple and inexpensive apparatus is provided for controlling the velocity of a work feed plate in a sewing machine operation. It is contemplated that the velocity control mechanism of the present invention may be utilized in other applications and that the connection of the work feed plate with ram 12 and control means 14 may be varied so long as the control means 14 is connected to the plate to resist movement by ram 12. Further, it is contemplated that the number of ports and pistons in cylinder 40 may be varied to achieve a variety of movement patterns of the work element or plate.

Accordingly, while illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, in that various changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of this invention.

What is claimed is:

l. A device for reciprocating a work element between first and second positions at varying speeds in a predetermined sequence comprising, means operably connected to said work element for applying a uniform force to said element to move the element between said first and said second positions, and means for variably resisting movement of said work element in accordance with said predetermined sequence to vary the speed of movement of said element from said first to said second position, said resisting means including a hydraulic control cylinder having at least two ports therein, a fluid reservoir in communication with said cylinder through said ports, and plunger means in said cylinder operatively connected to said work element and cooperating with fluid in said cylinder for resisting movement of said work element by said force applying means and for sequentially returning said fluid to said reservoir from said cylinder as said work element is moved from its first to its second position by said force applying means, initially through only one of said ports,

then through both ports, whereby movement of said work element is variably resisted and said work element is moved faster between said first and second positions when fluid is returned to said reservoir through both of said ports, than when fluid is returned to said reservoir through only said one port.

2. A device as defined in claim 1 wherein said reservoir is connected to said cylinder ports by independent conduit means, and said conduit means include restrictions therein resisting fluid flow therethrough.

3. A device as defined in claim 2 wherein said force applying means comprises a double acting hydraulic ram.

4. A device as defined in claim 2 including check valve means interconnecting said reservoir to said cylinder for permitting free flow of fluid therethrough from said reservoir to said cylinder as said work element is returned by said force applying means from its second to its first position.

5. A device for reciprocating a work element between first and second positions at varying speeds in a predetermined sequence comprising, means operably connected to said work element for applying a uniform force and said element to move the element between said first to said second positions and means for variably resisting movement of said work element in accordance with said predetermined sequence to vary the speed of movement of said element from said first to said second position, said resisting means including a hydraulic control cylinder having at least two ports therein, a fluid reservoir in communication with said cylinder through said ports, and plunger means in said cylinder operatively connected to said work element and cooperating with fluid in said cylinder for resisting movement of said work element by said force applying means and for sequentially returning fluid to said reservoir from said cylinder as said work element moves from its first to its second position, initially through only one of said ports, then through both ports, and finally through only said one port whereby movement of said work element is variably resisted and said work element is moved faster between said first and second positions when fluid is returned to said reservoir through both of said ports than when fluid is returned to said reservoir through only said one port during the initial and final portions of movement thereof.

6. A device as defined in claim 5 wherein said reservoir is connected to said cylinder ports by independent conduit means, and said conduit means include restrictions therein resisting fluid flow therethrough.

7. A device as defined in claim 5 wherein said force applying means comprises a double acting hydraulic ram.

8. A device as defined in claim 5 including check valve means interconnecting said reservoir to said cylinder for permitting free flow of fluid therethrough from said reservoir to said cylinder as said work element is returned by said force applying means from its second to its first position.

9. A device as described in claim 6 wherein said plunger means comprises a pair of spaced operatively interconnected pistons defining a first fluid chamber therebetween in said cylinder, said plunger means being moved with said element by the force applying means from a first to a second position corresponding to the first and second positions of said element to selectively close said one port at the initial and final portions of movement of said element.

10. A device as defined in claim 9 wherein the other of said ports is located adjacent one end of said cylinder and said one end defines a second fluid chamber with said one piston, the latter having at least one bleed bore therein to provide communication between said first and second chambers for equalizing fluid pressure therein.

11. In a sewing machine having a work feed plate for supporting and moving an article to be sewn beneath the sewing head of the machine and wherein the feed plate is mounted for reciprocal movement between first and second positions at varying speeds and in a predetermined sequence for varying the spacing between stitches sewn into the fabric, means for reciprocating the plate at varying speeds comprising a ram operatively connected to said plate for applying a uniform force thereto to move the plate between said first to said second positions and means for variably resisting movement of said plate in accordance with said predetermined sequence to vary the speed of movement of said plate from said first to said second position and thereby vary said stitch spacing including, a hydraulic control cylinder having at least first and second ports therein, a plunger in said cylinder operatively connected to said work feed plate for movement therewith under the influence of said ram between first and second positions corresponding respectively to the first and second positions of said plate, said plunger having first and second spaced operatively interconnected pistons defining a first fluid chamber in said cylinder, a

reservoir, independent conduit means respectively connecting said reservoir to said ports, said first ports being located for communication with said first chamber and said second port being located for communication with a second fluid chamber defined by said first piston and one end of said cylinder, said first piston having at least one bleed bore therein to provide communication between said first and second chambers for equalizing fluid pressure therein and said pistons cooperating with fluid in said cylinder for resisting movement of said plate by said ram in accordance with said predetermined sequence, said first piston closing said first port in the first position thereof and forcing fluid in said second chamber through said second port during initial movement of said plunger from its first to its second position and opening said first port to said first chamber after said initial movement, movement of said second piston thereafter forcing fluid in said second chamber through said first port to said reservoir, while movement of said first piston continues to force fluid to said reservoir through said port, thereby decreasing the resistance to movement of said plate, said second piston thereafter being moved into position to close said first port as said plunger approaches its second position while said first piston continues to force fluid to said reservoir through said second port, whereby the speed of movement of said plate is sequentially varied to provide relatively small spacing between stitches at the beginning and ends of movement of said plate from its first to its second position and wider spacing between stitches at the intermediate portion of said movement.

12. A device as defined in claim 11 wherein said conduits have fluid flow restrictors therein.

13. A device as defined in claim 12 wherein said ram is a double acting ram adapted to return said plate from its second to its first position.

14. A device as defined in claim 13 wherein one of said conduits includes a conduit portion bypassing the flow restrictor therein and a check valve in said bypass permitting free return of fluid in said reservoir to said cylinder as said plate and plunger are returned from their second to their first'positions. 

1. A device for reciprocating a work element between first and second positions at varying speeds in a predetermined sequence comprising, means operably connected to said work element for applying a uniform force to said element to move the element between said first and said second positions, and means for variably resisting movement of said work element in accordance with said predetermined sequence to vary the speed of movement of said element from said first to said second position, said resisting means including a hydraulic control cylinder having at least two ports therein, a fluid reservoir in communication with said cylinder through said ports, and plunger means in said cylinder operatively connected to said work element and cooperating with fluid in said cylinder for resisting movement of said work element by said force applying means and for sequentially returning said fluid to said reservoir from said cylinder as said work element is moved from its first to its second position by said force applying means, initially through only one of said ports, then through both ports, whereby movement of said work element is variably resisted and said work element is moved faster between said first and second positions when fluid is returned to said reservoir through both of said ports, than when fluid is returned to said reservoir through only said one port.
 2. A device as defined in claim 1 wherein said reservoir is connected to said cylinder ports by independent conduit means, and said conduit means include restrictions therein resisting fluid flow therethrough.
 3. A device as defined in claim 2 wherein said force applying means comprises a double acting hydraulic ram.
 4. A device as defined in claim 2 including check valve means interconnecting said reservoir to said cylinder for permitting free flow of fluid therethrough from said reservoir to said cylinder as said work element is returned by said force applying means from its second to its first position.
 5. A device for reciprocating a work element between first and second positions at varying speeds in a predetermined sequence comprising, means operably connected to said work element for applying a uniform force and said element to move the element between said first to said second positions and means for variably resisting movement of said work element in accordance with said predetermined sequence to vary the speed of movement of said element from said first to said second position, said resisting means including a hydraulic control cylinder having at least two ports therein, a fluid reservoir in communication with said cylinder through said ports, and plunger means in said cylinder operatively connected to said work element and cooperating with fluid in said cylinder for resisting movement of said work element by said force applying means and for sequentially returning fluid to said reservoir from said cylinder as said work element moves from its first to its second position, initially through only one of said ports, then through both ports, and finally through only said one port whereby movement of said work element is variably resisted and said work element is moved faster between said first and second positions when fluid is returned to said reservoir through both of said ports than when fluid is returned to said reservoir through only said one port during the initial and final portions of movement thereof.
 6. A device as defined in claim 5 wherein said reservoir is connected to said cylinder ports by independent conduit means, and said conduit means include restrictions therein resisting fluid flow therethrough.
 7. A device as defined in claim 5 wherein said force applying means comprises a double acting hydraulic ram.
 8. A device as defined in claim 5 including check valve means interconnecting said reservoir to said cylinder for permitting free flow of fluid therethrough from said reservoir to said cylinder as said work element is returned by said force applying means from its second to its first position.
 9. A device as described in claim 6 wherein said plunger means comprises a pair of spaced operatively interconnected pistons defining a first fluid chamber therebetween in said cylinder, said plunger means being moved with said element by the force applying means from a first to a second position corresponding to the first and second positions of said element to selectively close said one port at the initial and final portions of movement of said element.
 10. A device as defined in claim 9 wherein the other of said ports is located adjacent one end of said cylinder and said one end defines a second fluid chamber with said one piston, the latter having at least one bleed bore therein to provide communication between said first and second chambers for equalizing fluid pressure therein.
 11. In a sewing machine having a work feed plate for supporting and moving an article to be sewn beneath the sewing head of the machine and wherein the feed plate is mounted for reciprocal movement between first and second positions at varying speeds and in a predetermined sequence for varying the spacing between stitches sewn into the fabric, means for reciprocating the plate at varying speeds comprising a ram operatively connected to said plate for applying a uniform force thereto to move the plate between said first to said second positions and means for variably resisting movement of said plate in accordance with said predetermined sequence to vary the speed of movement of said plate from said first to said second position and thereby vary said stitch spacing including, a hydraulic control cylinder having at least first and second ports therein, a plunger in said cylinder operatively connected to said work feed plate for movement therewith under the influence of said ram between first and second positions corresponding respectively to the first and second positions of said plate, said plunger having first and second spaced operatively interconnected pistons defining a first fluid chamber in said cylinder, a reservoir, independent conduit means respectively connecting said reservoir to said ports, said first ports being located for communication with said first chamber and said second port being located for communication with a second fluid chamber defined by said first piston and one end of said cylinder, said first piston having at least one bleed bore therein to provide communication between said first and second chambers for equalizing fluid pressure therein and said pistons cooperating with fluid in said cylinder for resisting movement of said plate by said ram in accordance with said predetermined sequence, said first piston closing said first port in the first position thereof and forcing fluid in said second chamber through said second port during initial movement of said plunger from its first to its second position and opening said first port to said first chamber after said initial movement, movement of said second piston thereafter forcing fluid in said second chamber through said first port to said reservoir, while movement of said first piston continues to force fluid to said reservoir through said port, thereby decreasing the resistance to movement of said plate, said second piston thereafter being moved into position to close said first port as said plunger approaches its second position while said first piston continues to force fluid to said reservoir through said second port, whereby the speed of movement of said plate is sequentially varied to provide relatively small spacing between stitches at the beginning and ends of movement of said plate from its first to its second position and wider spacing between stitches at the intermediate portion of said movement.
 12. A device as defined in claim 11 wherein said conduits have fluid flow restrictors therein.
 13. A device as defined in claim 12 wherein said ram is a double acting ram adapted to return said plate from its second to its first position.
 14. A device as defined in claim 13 wherein one of said conduits includes a conduit portion bypassing the flow restrictor therein and a check valve in said bypass permitting free return of fluid in said reservoir to said cylinder as said plate and plunger are returned from their second to their first positions. 